Radar, AA, No4 Mk1

Radar, AA, No4 Mk1


Mobile equipment for early warning of aircraft to indicate the approximate range and bearing to equipment radar AA No3 Mk1.




Four-wheeled trailer with steel and wooden cabin for Tx and Rx. Rotatable aerial array mounted on steel frame-work, collapsible for travelling. Known as the ZPI (Zone Position Indicator) part of the Canadian GLIII(C) System.
The APF was the No3 Mk1.

Presentation Unit

Range & Bearing : PPI type (in APF cabin, see Radar, AA, No3 Mk1)
22 rpm radial sweep.

Physical data
Length20' operational
 20'9" travelling
Width7'8" operational
 7'8" travelling
Height25'6" operational
 10'8" travelling
Turning circle30'0"
Ground clearance12"
Wading depth2'3" still water
Bridge class4/6
Towing vehicleLorry, 4ton, FWD
Electrical data
Operational wavelength145-155 Mc/s
I.F. freq31Mc/s
Receiver bandwidth1Mc/s at -3dB
Tx power output120 kW
Tx pulse width2/4/6 us
Recurrence freq800 to 1200 c/s
Detection accuracyrange +/- 1000yds
 azimuth +/- 2deg
Detection range50,000yds
Data Transmissionby magslips

Antenna System

Common T and R.
Horizontal 7-element co-linear array and parasitic reflectors with vertical 6-element array intersparsed.
Open wire feeders.
Turning gear : Aerial array rotated at 22rpm by 3/4 h.p. single phase motor.

Power Supplies

115V/230V ac 50c/s or 60c/s, single phase.
Normally supplied by a Cumminss diesel 31 kVA generator.


Technical : 1
PPI operator : 1


Not yet fitted (1944)


Careful siting required for long range and freedom from ground echoes.
Receiver IF signals fed to PPI unit in APF cabin by concentric cable.

References and Sources

More No4 Mk1 pictures

No4 Mk1 radar. Production model ZPI trailer showing elliptically polarized antenna. Early model ZPI in the background.

Production model ZPI trailer showing elliptically polarized antenna. Early model ZPI in the background.

No4 Mk1 radar getting ready for shipment

Ten No4 Mk1 radar trailers getting ready for shipment

No4 Mk1 radar residing at the Royal canadian Artillery Museum, Shilo, Canada.

No4 Mk1 residing at the Royal canadian Artillery Museum, Shilo, Canada.

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